Apparatus for and method of forming image using oscillation mirror

ABSTRACT

As a scanning light beam which is scanning and traveling away from an effective image region moves passed the location of a sensor, a horizontal synchronizing signal Hsync is obtained as a first detection signal. A deflection mirror surface turns around, thereby reversing the direction in which the scanning light beam scans. This scanning light beam therefore scans an effective image region IR, and a latent image forming operation using this scanning light beam is controlled based on the horizontal synchronizing signal Hsync. Hence, there is a relatively long period of time (T 4 +T 5 ) since the horizontal synchronizing signal Hsync is obtained until formation of a latent image starts in accordance with the signal Hsync. This secures sufficient time for control of the latent image forming operation based on the horizontal synchronizing signal Hsync, and hence, realizes the latent image forming operation as desired during the time T 6.

CROSS REFERENCE TO RELATED APPLICATION

The disclosure of Japanese Patent Applications enumerated belowincluding specification, drawings and claims is incorporated herein byreference in its entirety:

No. 2004-170831 filed Jun. 9, 2004; and

No. 2004-170831 filed Jun. 9, 2004.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an image forming apparatus, an imageforming method and a light amount adjusting method within the apparatus.In the apparatus, a deflecting mirror or a oscillation mirror makes alight beam from a light source scan on an effective image region of alatent image carrier, thereby forming a latent image in the effectiveimage region.

2. Description of the Related Art

In a known apparatus, a deflector deflects a light beam emitted from alight source, the light beam scans on a latent image carrier such as aphotosensitive drum and a latent image is formed. In the image formingapparatus described in Japanese Patent Application Laid-Open Gazette No.S63-102545, No. H5-276336 or the like for instance, a semiconductorlaser is used as a light source, and the semiconductor laser emits alight beam having a light intensity which corresponds to an imagesignal. After deflected by a deflector such as a polygon mirror, thelight beam modulated in this manner is guided to a latent image carriervia an optical element such as a lens and scans on the latent imagecarrier along a main scanning direction. As a result, a latent imagecorresponding to the image signal is formed on the latent image carrier.

Further, in this image forming apparatus, an optical detection sensorsuch as a photosensor is disposed on a scanning path of the light beam,for the purpose of forming a favorable image. In short, the opticaldetection sensor detects that the light beam scans passed the startingpoint of the scanning path, and based on the result of the detection,the timing to start optical modulation is adjusted. In this conventionalapparatus, the starting point at which the light beam starts scanning isdetected in this manner and a latent image forming operation isaccordingly controlled.

In addition, this image forming apparatus comprises an APC circuit toapproximately coincide a light amount of the light beam emitted from thesemiconductor laser with a reference light amount. The APC circuitcompares the reference light amount determined in advance with theamount of the emitted light beam detected by a photo diode built in thesemiconductor laser, and controls such that the amount of the light beamcoincides with the reference light amount. To be more specific, feedingof an initial pulse which is for activation of the semiconductor laserinitiates adjustment of the amount of the light emitted from thesemiconductor laser so that the light amount coincides with thereference light amount. This light amount adjusting operation isexecuted during a period in which the light beam scans one line. Whenthe amount of the emitted light becomes equal to the reference lightamount, the light amount adjustment is stopped, and a latent image isformed line by line through light modulation. The light modulation isperformed by controlling turning on and off of the semiconductor laserin accordance with the image signal. During this, the amount of theemitted light beam is equal to the reference light amount when thesemiconductor laser is ON but zero when the semiconductor laser is OFF.

Upon creation of the latent image for one page, the APC circuit executesthe light amount adjustment once again and matches the amount of thelight from the semiconductor laser with the reference light amount.After the light amount adjustment is stopped, a latent image for nextone page is formed.

SUMMARY OF THE INVENTION

By the way, an image forming apparatus which uses an oscillation mirrorrather than a polygon mirror as a deflector is known. In such anapparatus as well, the starting point where the light beam startsscanning may be detected for control of the latent image formingoperation as in the conventional apparatus described above. However, thecontrol should preferably consider an operation characteristic. That is,with respect to a light beam deflected by a polygon mirror, it ispossible to move the light beam only in a direction which corresponds tothe direction of rotations of the polygon mirror but it is not possiblefor the light to scan in the opposite direction. In contrast, where anoscillation mirror is used, a light beam can reciprocally move in a mainscanning direction. Control of the latent image forming operationutilizing such a characteristic is therefore desirable. For example, inthis type of image forming apparatus, an effective image region, namely,an area where a latent image is to be formed is defined in advance on alatent image carrier. An optical detection sensor detects a light beambefore the light beam arrives at the effective image region. And then,based on the result of the detection, various types of control isimplemented such as setting of the timing to modulate the light,confirmation of the operation performed by the deflector and detectionof an error. Hence, for favorable execution of this latent image formingoperation, it is desirable that there is a long time since the opticaldetection sensor detects the light beam until the light beam reaches theeffective image region.

For the apparatus which uses the polygon mirror to meet thisrequirement, the distance between the optical detection sensor and theeffective image region needs be long. Increase of this distance howevernecessitates enlarging the scanning area of the polygon mirror andtherefore inevitably leads to increase of the sizes of opticalcomponents including the polygon mirror and optical elements and thesize of the apparatus.

Meanwhile, as a solution to various problems associated with use of apolygon mirror as a deflector, an apparatus equipped with an oscillationmirror which is manufactured using a micro machining technique has beenproposed. In this apparatus, as an optical deflector, a driver coil, adeflection mirror surface and a ligament are formed within a frame allof which are one integrated structure obtained by photolithographicprocessing, etching and the like of a substrate made of crystal, glass,silicon, etc. When a driver applies a voltage upon the driver coil, thedeflection mirror surface oscillates about an oscillation axis which isapproximately orthogonal to a main scanning direction, whereby a lightbeam incident upon the deflection mirror surface is deflected. Further,in the case of an oscillation mirror of this type, to secure a widescanning area, the frequency of a drive signal fed to the driver coil isalmost the same as the resonant frequency of the oscillation mirror, andat this frequency, the deflection mirror surface is made to resonate.Due to this, a change of the resonant frequency caused by a change in anenvironment where the oscillation mirror is used, e.g., a change intemperature deviates the resonant frequency from the drive frequency andchanges the oscillation amplitude. In the event that an oscillationmirror which resonates is used, it is therefore particularly importantfor a favorable latent image forming operation to confirm that theoscillation mirror oscillates without fail and to securely notice anychange of the oscillation amplitude. The conventional techniques howeverdo not sufficiently address these issues.

While the light beam successively scans the latent image carrier to forma latent image for one page in the conventional apparatus above, the APCcircuit does not adjust the amount of light during this. In short, alatent image is formed based upon the assumption that the amount of thelight emitted from the semiconductor laser remains unchanged while thelight scans for one page. Despite this, it is difficult to perfectlyprevent the amount of the emitted light from changing, and a change ofthe amount of light is sometimes influential.

A primary object of the present invention is to realize favorableexecution of a latent image forming operation within an image formingapparatus in which a light beam emitted from a light source scans on aneffective image region of a latent image carrier and a latent image isformed in the effective image region.

Other object of the present invention is to adjust the amount of thelight beam while a latent image is being formed through successivescanning with the light beam and to thereby stably form the latentimage.

The present invention is directed to an image forming apparatus, amethod of forming an image using the apparatus and a method of adjustingan amount of light within the apparatus. The image forming apparatuscomprises: a latent image carrier which has an effective image regionover a predetermined width along a main scanning direction; and a latentimage forming section which, using a deflection mirror surface whichoscillates, makes a light beam from a light source scan a secondscanning area which is wider than a first scanning area whichcorresponds to the effective image region along the main scanningdirection, and guides the scanning light beam in the first scanning areatoward the effective image region, thereby forming a latent image in theeffective image region.

According to a first aspect of the present invention, a first light beamwhich is scanning and traveling away from the effective image region isdetected. The operation of forming a latent image is controlled inaccordance with the result of detection of the first light beam.

According to a second aspect of the present invention, while the lightbeam moves outside the first scanning area but within the secondscanning area, the amount of this light beam is adjusted.

The above and further objects and novel features of the invention willmore fully appear from the following detailed description when the sameis read in connection with the accompanying drawing. It is to beexpressly understood, however, that the drawing is for purpose ofillustration only and is not intended as a definition of the limits ofthe invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a drawing which shows a first embodiment of an image formingapparatus according to the present invention;

FIG. 2 is a block diagram which shows the electric structure of theimage forming apparatus which is shown in FIG. 1;

FIG. 3 is a main-scanning cross sectional view showing the structure ofthe exposure unit which is disposed in the image forming apparatus whichis shown in FIG. 1;

FIG. 4 is a diagram which shows a scanning area in the exposure unit;

FIG. 5 is a diagram which shows the structures of the exposure unit andthe exposure controller;

FIG. 6 is a graph which shows a relationship between a mirror drivesignal and amplitude of a deflection mirror surface;

FIGS. 7A and 7B are drawings of the sensing operation of sensing thescanning light beam in the image forming apparatus which is shown inFIG. 1;

FIG. 8 is a flow chart of a latent image forming operation and a lightamount adjusting operation performed in the second embodiment;

FIGS. 9A and 9B are drawings of a sensing operation of sensing ascanning light beam and the light amount adjusting operation in thesecond embodiment;

FIG. 10 is a flow chart of a latent image forming operation and a lightamount adjusting operation performed in the third embodiment;

FIGS. 11A and 11B are drawings of a sensing operation of sensing ascanning light beam and the light amount adjusting operation in thethird embodiment; and

FIG. 12 is a drawing which shows one other embodiment of an imageforming apparatus according to the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 is a drawing which shows a first embodiment of an image formingapparatus according to the present invention. FIG. 2 is a block diagramwhich shows the electric structure of the image forming apparatus whichis shown in FIG. 1. This image forming apparatus is a color printer ofthe so-called 4-cycle type. In this image forming apparatus, when aprint command is fed to a main controller 11 from an external apparatussuch as a host computer in response to a user's image formation request,an engine controller 10 controls respective portions of an engine partEG in accordance with the print instruction received from the maincontroller 11 of a CPU 111, and an image which corresponds to the printinstruction is formed on a sheet which may be a copy paper, a transferpaper, a plain paper or a transparency for an overhead projector.

In the engine part EG, a photosensitive member 2 is disposed so that thephotosensitive member 2 can freely rotate in the arrow direction (subscanning direction) shown in FIG. 1. The photosensitive member 2corresponds to a latent image carrier of the present invention. Aroundthe photosensitive member 2, a charger unit 3, a rotary developer unit 4and a cleaner (not shown) are disposed along the direction in which thephotosensitive member rotates. A charging controller 103 is electricallyconnected with the charger unit 3, for application of a predeterminedcharging bias upon the charger unit 3. The bias application uniformlycharges an outer circumferential surface of the photosensitive member 2to a predetermined surface potential. The photosensitive member 2, thecharger unit 3 and the cleaner form one integrated photosensitive membercartridge which can be freely attached to and detached from a main body5 as one integrated unit.

An exposure unit 6 emits a light beam L toward the outer circumferentialsurface of the photosensitive member 2 thus charged by the charger unit3. The exposure unit 6 makes the light beam L scan on the photosensitivemember 2 based on an electric signal from an exposure controller whichwill be described later, whereby an electrostatic image which reflectsan image signal is formed. The exposure unit 6 is thus a latent imageforming section according to the present invention, and the structureand operations of the exposure unit will be described in detail later.

The developer unit 4 develops thus formed electrostatic latent imagewith toner. In other words, in this embodiment, the developer unit 4comprises a support frame 40 which is axially disposed for freerotations, and also a yellow developer 4Y, a magenta developer 4M, acyan developer 4C and a black developer 4K which house toner of therespective colors and are formed as cartridges which are freelyattachable to and detachable from the support frame 40. The developerunit 4 is driven into rotations in response to a control command givenfrom a developer controller 104 of the engine controller 10. When thedevelopers 4Y, 4C, 4M and 4K are selectively positioned at apredetermined developing position which abuts on the photosensitivemember 2 or is faced with the photosensitive member 2 over apredetermined gap, toner of the color corresponding to the selecteddeveloper is supplied onto the surface of the photosensitive member 2 bya developer roller 44 which carries the toner of the selected color. Asa result, the electrostatic latent image on the photosensitive member 2is visualized in the selected toner color.

A toner image developed by the developer unit 4 in the manner above isprimarily transferred onto an intermediate transfer belt 71 of atransfer unit 7 in a primary transfer region TR1. The transfer unit 7comprises the intermediate transfer belt 71 which runs across aplurality of rollers 72, 73, etc., and a driver (not shown) which drivesthe roller 73 into rotations to thereby rotate the intermediate transferbelt 71 in a predetermined rotation direction.

Further, there are a transfer belt cleaner (not shown), a density sensor76 (FIG. 2) and a vertical synchronization sensor 77 (FIG. 2) in thevicinity of the roller 72. Of these, the density sensor 76 is disposedfacing a surface of the intermediate transfer belt 71 and measures theoptical density of a patch image formed on an outer circumferentialsurface of the intermediate transfer belt 71. Meanwhile, the verticalsynchronization sensor 77 is a sensor which detects a reference positionof the intermediate transfer belt 71, and serves as a verticalsynchronization sensor for obtaining a synchronizing signal outputted inrelation to rotations of the intermediate transfer belt 71 in the subscanning direction, namely, a vertical synchronizing signal Vsync. Inthis apparatus, for the purpose of aligning the timing at which therespective portions operate and accurately overlaying toner images ofthe respective colors on top of each other, the respective portions ofthe apparatus operate under the control of the vertical synchronizingsignal Vsync.

For transfer of color images on sheets, the toner images of therespective colors formed on the photosensitive member 2 are overlaideach other on the intermediate transfer belt 71, thereby forming colorimages which will then be secondarily transferred onto sheets taken outone by one from a cassette 8 and transported on a transportation path Fto a secondary transfer region TR2.

At this stage, in order to properly transfer the images carried by theintermediate transfer belt 71 onto a sheet at a predetermined position,the timing of feeding the sheet to the secondary transfer region TR2 iscontrolled. To be specific, there is a gate roller 81 disposed in frontof the secondary transfer region TR2 on the transportation path F, andas the gate roller 81 rotates in synchronization to the timing ofrotations of the intermediate transfer belt 71, the sheet is fed intothe secondary transfer region TR2 at predetermined timing.

Further, the sheet now bearing the color image is transported to adischarge tray part 51, which is disposed to a top surface portion ofthe main body 5, through a fixing unit 9 and a discharge roller 82. Whenimages are to be formed on the both surfaces of a sheet, the dischargeroller 82 moves the sheet seating an image on its one surface in themanner above in a switch back motion. The sheet is therefore transportedalong a reverse transportation path FR. While the sheet is returned backto the transportation path F again before arriving at the gate roller81, the surface of the sheet which abuts on the intermediate transferbelt 71 in the secondary transfer region TR2 and is to receive atransferred image is, at this stage, the opposite surface to the surfacewhich already bears the image. In this fashion, it is possible to formimages on the both surfaces of the sheet.

In FIG. 2, denoted at 113 is an image memory disposed in the maincontroller 11 for storage of image data fed from an external apparatussuch as a host computer via an interface 112. Denoted at 106 is a ROMwhich stores a computation program executed by a CPU 101, control datafor control of the engine part EG, etc. Denoted at 107 is a RAM whichtemporarily stores a computation result derived by the CPU 101, otherdata, etc.

FIG. 3 is a main-scanning cross sectional view showing the structure ofthe exposure unit which is disposed in the image forming apparatus whichis shown in FIG. 1. FIG. 4 is a diagram which shows a scanning area inthe exposure unit. FIG. 5 is a diagram which shows the structures of theexposure unit and the exposure controller. The structure and operationsof the exposure unit 6 will now be described in detail with reference tothese drawings.

This exposure unit 6 comprises an exposure housing 61. A single lasersource 62 is fixed to the exposure housing 61, permitting emission of alight beam from the laser source 62. The laser source 62 is electricallyconnected with a light source driver 1021 of an exposure controller 102as shown in FIG. 5. The light source driver 1021 supplies a light sourcedrive signal corresponding to an image signal to the laser source 62.ON/OFF of the laser source 62 is controlled based on the light sourcedrive signal, whereby the light beam modulated in accordance with imagedata from the laser source 62 is emitted forward. Further, as describedlater, ON/OFF of the laser source 62 is controlled at the edges of ascanning area for APC control (adjustment of the amount of light) duringacquisition of a horizontal synchronizing signal Hsync and successiveformation of a latent line image, which also results in forward emissionof the light beam from the laser source 62.

When emitting the light beam forward, the laser source 62 also emitstoward the rear side a light beam for monitoring of the amount of light.A sensor 621 disposed inside a case for the laser source 62 receivesthis light beam. The sensor 621 is formed by a photo diode or the likeand electrically connected with an APC circuit 1022 of the exposurecontroller 102. Hence, as the laser source 62 turns on, the light beamfor exposure is emitted forward while the rear-emission light beamimpinges upon the sensor 621 at the same time and a signal correspondingto the amount of the light beam is fed to the APC circuit 1022. The APCcircuit 1022 compares a reference light amount set in advance with theamount of the light detected by the sensor 621, and controls the lightsource driver 1021 such that the amount of the light beam from the lasersource 62 coincides with the reference light amount. In this embodiment,the APC circuit 1022 thus functions as the “light amount adjuster” ofthe invention.

Further, to make the light beam from the laser source 62 scan and exposethe surface of the photosensitive member 2 (surface-to-be-scanned), acollimator lens 631, a cylindrical lens 632, a mirror 64, a deflector65, a scanning lens 66 and a return mirror 68 are disposed inside theexposure housing 61. In other words, after shaped into collimated lightof a proper size by the collimator lens 631, the light beam from thelaser source 62 impinges upon the cylindrical lens 632 which has poweronly in a sub scanning direction Y This collimated light is thenconverged only in the sub scanning direction Y and imaged in the shapeof a line in the vicinity of a deflection mirror surface 651 of thedeflector 65. In this embodiment, the collimator lens 631 and thecylindrical lens 632 thus function as a first optical system 63 whichshapes the light beam from the laser source 62 into an elongated crosssectional shape which is long in a main scanning direction X and makesthe light beam impinge upon the deflection mirror surface 651.

This deflector 65 is obtained using a micro machining technique which isan application of semiconductor manufacturing techniques and which aimsat forming an integrated micro machine on a semiconductor substrate, andformed by an oscillation mirror which resonates. In other words, thedeflector 65 is capable of, at its deflection mirror surface 651 whichresonates, deflecting the light beam along the main scanning directionX. To be more specific, the deflection mirror surface 651 is axiallysupported such that it can freely oscillate about an oscillation shaft(torsion spring) which is approximately orthogonal to the main scanningdirection X. When the deflection mirror surface 651 is subjected toexternal force exerted from an activator, the deflection mirror surface651 oscillates about the oscillation shaft. The activator exertselectrostatic, electromagnetic or mechanical external force upon thedeflection mirror surface 651 based on a mirror drive signal from amirror driver 1023 of the exposure controller 102, thereby oscillatingthe deflection mirror surface 651 at the frequency of the mirror drivesignal (FIG. 6). However, as shown in FIG. 6, the deflection mirrorsurface 651 oscillates after the time gap ΔTd from the receipt of themirror drive signal. The activator may drive utilizing electrostaticabsorption, electromagnetic force, mechanical force or the like, eachdriving method of which is already known and will not be described here.

The light beam deflected by the deflection mirror surface 651 of thedeflector 65 heads toward a scanning lens 66 at a maximum angle ofamplitude θmax as shown in FIG. 4. In this embodiment, the scanning lens66 is structured so that its F-value remains approximately the sameacross all of an effective image region IR of a photosensitive member 2.Hence, the light beam deflected toward the scanning lens 66 is imagedvia the scanning lens 66 as spots having approximately identicaldiameters within the effective image region IR of the photosensitivemember 2. In this manner, as the light beam scans parallel to the mainscanning direction X, a latent image shaped like a line elongating inthe main scanning direction X is formed in the effective image region IRon the photosensitive member 2. In this embodiment, a scanning area SR2which is made scannable by the deflector 65 (the “second scanning area”of the invention) is wider than a scanning area SR1 within the effectiveimage region IR where the light beam scans (the “first scanning area” ofthe invention) as shown in FIG. 4. The first scanning area SR1 islocated approximately at the center of the second scanning area SR2, andis approximately symmetrical with respect to an optical axis L0. In FIG.4, the symbol θir denotes the angle of amplitude of the deflectionmirror surface 651 corresponding to the edges of the effective imageregion IR, and the symbol θs denotes the angle of amplitude of thedeflection mirror surface 651 corresponding to horizontalsynchronization sensors which will be described next.

Further, in this embodiment, as shown in FIG. 3, return mirrors 69 a and69 b guide the scanning light beam to horizontal synchronization sensors60A and 60B at the both ends of the scanning path of the scanning lightbeam. The return mirrors 69 a and 69 b are disposed respectively at theboth edges of the second scanning area SR2, and within the secondscanning area SR2, guide the scanning light beam to the horizontalsynchronization sensors 60A and 60B whenever the scanning light beamexits the first scanning area SR1. Receiving the scanning light beam,the horizontal synchronization sensors 60A and 60B output signals uponarrival of the scanning light beam at the sensor positions (the angle ofamplitude θs). The return mirrors 69 a and 69 b are approximatelysymmetrical with respect to the optical axis L0 as it is when the lightbeam scans an approximately center of the effective image region IR. Itis therefore considered that the horizontal synchronization sensors 60Aand 60B are disposed approximately symmetrical with respect to theoptical axis.

The signals indicative of detection of the scanning light beam by thehorizontal synchronization sensors 60A and 60B are transmitted to ameasuring unit 1024 of the exposure controller 102, and this measuringunit calculates the scanning time in which the light beam scans theeffective image region IR. The scanning time calculated by the measuringunit 1024 is transmitted to the mirror driver 1023. The mirror driver1023 is capable of changing and setting a drive condition for thedeflection mirror surface 651 in accordance with the transmittedscanning time. In addition, in this embodiment, the horizontalsynchronization sensors 60A and 60B function as a horizontalsynchronization reading sensor which is for obtaining a synchronizingsignal based on which the light beam scans the effective image region IRalong the main scanning direction X, namely, a horizontal synchronizingsignal Hsync. The operation of sensing the scanning light beam performedby the horizontal synchronization sensors 60A and 60B will now bedescribed in detail.

FIGS. 7A and 7B are drawings of the sensing operation of sensing thescanning light beam in the image forming apparatus which is shown inFIG. 1. FIG. 7A is a timing chart of the sensing operation near thesensors, while FIG. 7B is a drawing which schematically shows ON/OFF ofthe laser near the sensors. Although described below is the sensingoperation by the sensor 60A in the scanning area, the sensing operationby the sensor 60B is exactly the same.

While a latent image is being formed with the light beam scanning theeffective image region IR on the photosensitive member 2 (time T1), thelight source drive signal corresponding to the image signal is fed tothe laser source 62 from the light source driver 1021 and the lasersource 62 turns on in accordance with the image signal as describedearlier. As a result, a latent image corresponding to the image signalis formed in the effective image region IR of the photosensitive member2. As the scanning light beam moves passed the effective image regionIR, the light source drive signal falls down to the L-level and thelaser source 62 turns off. After this, the laser source 62 remainsturned off immediately before the angle of amplitude of the deflectionmirror surface 651 reaches θs (time T2).

The light source drive signal rises to the H-level after the time T2, sothat the laser source 62 turns on. The deflection mirror surface 651then makes the light beam (first light beam) from the laser source 62scan, and the sensor 60A outputs the horizontal synchronizing signalHsync when the light beam moves passed the sensor position (the angle ofamplitude θs). The light source drive signal falls down to the L-levelagain after this sensor output, and the laser source 62 turns off (timeT3). Following this, when the angle of amplitude of the deflectionmirror surface 651 reaches the maximum angle of amplitude θmax, thedeflection mirror surface 651 turns around (time T4). Over the time T5,the angle of amplitude of the deflection mirror surface 651 reaches theangle of amplitude θir. Throughout the time (T4+T5), the laser source 62remains turned off.

The next latent image forming operation is thereafter started inresponse to the horizontal synchronizing signal Hsync described above.That is, in synchronization to the horizontal synchronizing signalHsync, the light source drive signal corresponding to the image signalis supplied to the laser source 62 from the light source driver 1021 andthe laser source 62 turns on in accordance with the image signal (timeT6). As a result, a latent image corresponding to the image signal isformed in the effective image region IR of the photosensitive member 2.

As described above, in this embodiment, the deflection mirror surface651 makes the light beam from the laser source 62 scan reciprocallyalong the main scanning direction X. At the end of the scanning lightbeam, the horizontal synchronization sensor 60A acquires a firstdetection signal. In other words, as shown in FIGS. 7A and 7B, when thescanning light beam (first light beam) which is traveling away from theeffective image region IR moves passed the sensor position, thehorizontal synchronizing signal Hsync is obtained as the first detectionsignal. The deflection mirror surface 651 then turns around, reversingthe direction in which the scanning light beam scans. While thisscanning light beam (second light beam) therefore scans the effectiveimage region IR, the latent image forming operation with this scanninglight beam is controlled based on the horizontal synchronizing signalHsync. This ensures a relatively long time (T4+T5) since the acquisitionof the horizontal synchronizing signal Hsync until the start of latentimage formation based on the signal Hsync. It is therefore possible totake sufficient time for control of the latent image forming operationbased on the horizontal synchronizing signal Hsync and execute thelatent image forming operation favorably during the time T6.

The first detection signal may be detected with the laser source 62remaining continuously turned on between the latent image formingoperation (time T1) and the latent image forming operation (T6). It is aconscious choice that the laser source 62 turns on intermittently. To bemore specific, in the first embodiment, the laser source 62 turns offafter detection of the horizontal synchronizing signal Hsync which isthe first detection signal, and during the time (T4+T5) which is beforethe start of light modulation, the laser source 62 remains turned off.As the laser source 62 turns on and off under control in this manner, aneven more desirable latent image is formed. That is, the laser source 62turns on only at the timing needed for detection of the horizontalsynchronizing signal Hsync at a position outside the first scanning areaSR1 (the angle of amplitude θ:θir<θ<θmax), but otherwise turns off. Thisprevents development of stray light at a position outside the firstscanning area SR1 after detection of the horizontal synchronizing signalHsync, and effectively suppresses formation of a ghost image. It istherefore possible to form a more favorable latent image within theeffective image region IR.

Second Embodiment

FIG. 8 is a flow chart of a latent image forming operation and a lightamount adjusting operation performed in the second embodiment by theimage forming apparatus according to the invention. FIGS. 9A and 9B aredrawings of a sensing operation of sensing a scanning light beam and thelight amount adjusting operation in the second embodiment, of which FIG.9A is a timing chart of these operations near sensors, while FIG. 9B isa drawing which schematically shows ON/OFF of the laser near thesensors. Although described below is these operations by the sensor 60A,the operations by the sensor 60B are exactly the same. The basicstructure of the apparatus is identical except for the mode of control,and therefore, the structure of the apparatus will not be describedagain but will be denoted at the same reference symbols.

In this embodiment, as the scanning light beam moves passed theeffective image region IR after completion of the latent image formingoperation for one line (Step S1), the light source drive signal fallsdown to the L-level and the laser source 62 turns off (Step S2). Afterthe time T2 (Step S3), the laser source 62 remains turned offimmediately before the angle of amplitude of the deflection mirrorsurface 651 reaches θs.

As the time T2 elapses, the light source drive signal rises to theH-level so that the laser source 62 turns on (Step S4). At this stage,when oscillations of the deflection mirror surface 651 are favorableones, the light beam (first light beam) from the laser source 62 is madeto scan by the deflection mirror surface 651, and the sensor 60A outputsthe horizontal synchronizing signal Hsync as the first detection signalwhen the light beam moves passed the sensor position (the angle ofamplitude θs). This results in the “YES” decision at Step S5 so that thesequence proceeds to Step S6 and the APC circuit 1022 starts APC control(adjustment of the amount of light). In other words, the APC circuit1022 controls the light source driver 1021 to thereby coincide thedetection signal from the sensor 621 of the laser source 62 with areference light amount determined in advance.

Further, in this embodiment, the laser source 62 stays turned on (T3+T4)so as to continue the APC control. Detection of a second detectionsignal and the APC control are executed in the following manner. Thatis, after the scanning light beam has moved passed the sensor 60A, thedeflection mirror surface 651 turns around at the maximum angle ofamplitude θmax and reverses the direction in which the scanning lightbeam scans. The scanning light beam (second light beam) then startstraveling toward the effective image region IR, and the sensor 60Aoutputs the horizontal synchronizing signal Hsync as the seconddetection signal when this light beam moves passed the sensor position(the angle of amplitude θs). This yields “YES” at Step S7 so that thesequence proceeds to Step S8 and the APC control ends.

After the time (T3+T4) since turning on of the laser source 62 (StepS9), the light source drive signal falls down to the L-level and thelaser source 62 turns off (time T5; Step S10). The sequence then returnsto Step S1 and the next latent image forming operation is started basedon the detection signal Hsync. In other words, in synchronization to thehorizontal synchronizing signal Hsync, the light source drive signalcorresponding to an image signal is fed to the laser source 62 from thelight source driver 1021 and the laser source 62 turns on in accordancewith the image signal (time T6). As a result, a latent imagecorresponding to the image signal is formed in the effective imageregion IR of the photosensitive member 2. The timing to start modulatingthe light may be controlled referring to either one of or both the firstdetection signal and the second detection signal.

In the event that oscillations of the deflection mirror surface 651 arenot favorable, the decision is “NO” at Step S5, Step S7, etc. Forinstance, a change in the environment of use may change the resonantfrequency of the deflector 65, in which case the resonant frequency willbecome different from the drive frequency and the oscillation amplitudemay greatly decrease. This may further cause malfunction of thedeflector 65. If the latent image forming operation is executed whileoscillations of the deflection mirror surface 651 are undesirable, thequality of images will deteriorate. Noting this, in this embodiment,both the first detection signal and the second detection signal aredetected for confirmation of desired oscillations of the deflectionmirror surface 651, and the latent image forming operation is thereafterexecuted in the manner described above. When one of the first detectionsignal and the second detection signal is not detected (“NO” at Step S5,Step S7, etc.), adjustment of the amount of light and the latent imageforming operation are stopped (Step S11). This is similar to the thirdembodiment which will be described later.

As described above, in this embodiment, the APC control (adjustment ofthe amount of light) is executed since formation of a latent line imageuntil formation of another latent line image, thereby adjusting theamount of the light beam emitted from the laser source 62. In short, thelight beam moves and scans over positions outside the effective imageregion IR (i.e., positions within the second scanning area SR2 butoutside the first scanning area SR1) and the amount of the light fromthe laser source 62 is adjusted. The amount of the light beam L is thusadjusted while the light beam is successively scanning and a latentimage is being formed within the effective image region IR, andtherefore, the latent image is formed stably.

In addition, as shown in FIGS. 9A and 9B, when the light beam (firstlight beam) which is traveling away from the effective image region IRmoves passed the sensor positions, the horizontal synchronizing signalHsync is obtained as the first detection signal and the APC control isstarted in response to this. Further, the deflection mirror surface 651turns around, thereby reversing the direction in which the scanninglight beam scans, and the horizontal synchronizing signal Hsync isobtained as the second detection signal when this scanning light beam(second light beam) moves passed the sensor positions, therebyterminating the APC control. Hence, it is possible to precisely controlthe timing to start and end the light amount adjusting operation.Moreover, since the amount of the light is adjusted continuously whilethe light beam moves passed the sensor positions twice, it is possibleto secure a long time for light amount adjustment and accurately adjustthe amount of the light.

The next latent image forming operation is executed after confirmingfrom the first and the second detection signals that the deflectionmirror surface 651 is oscillating as desired. It is therefore possibleto form a latent image always with the deflection mirror surface 651oscillating favorably without fail. Further, occurrence of a malfunctionis detected from these detection signals, and upon failure of confirmingoscillations of the deflection mirror surface 651, the light amountadjusting operation and the latent image forming operation are stopped.This securely prevents execution of an inappropriate latent imageforming operation and improper light amount adjusting operation.

Third Embodiment

FIG. 10 is a flow chart of a latent image forming operation and a lightamount adjusting operation performed in the third embodiment by theimage forming apparatus according to the invention. FIGS. 11A and 11Bare drawings of a sensing operation of sensing a scanning light beam andthe light amount adjusting operation in the third embodiment. A majordifference of the third embodiment from the second embodiment is thatthe laser source 62 turns on intermittently and the light amountadjusting operation is performed every time the light source turns on.In other words, in the third embodiment, as shown in FIGS. 11A and 11B,the laser source 62 is off while the angle of amplitude θ of thedeflection mirror surface 651 satisfies the relationship below at aposition outside the first scanning area SR1 (the angle of amplitudeθ:θir<θ<θmax):θs<θ≦θmaxAnd the amount of light is adjusted before and after this period inwhich the laser source 62 turns off (T4+T5). To be more specific, theamount of the light is adjusted over two stages as described below.First, the APC control (adjustment of the amount of light) is started ina similar manner to that in the second embodiment. That is, as thescanning light beam moves passed the effective image region IR aftercompletion of the latent image forming operation for one line (Step S1),the light source drive signal falls down to the L-level and the lasersource 62 turns off (Step S2). After the time T2 (Step S3), the lasersource 62 turns on (Step S4). The sensor 60A outputs the first detectionsignal Hsync as the light beam (first light beam) moves passed thesensor position (the angle of amplitude θs), and the APC circuit 1022starts the APC control (adjustment of the amount of light) (Step S6).

The APC control continues until the time T3 elapses since turning on ofthe laser source 62 (Step S61), and the laser source 62 turns off at thesame time as the end of the APC control (Step S62). The first lightamount adjustment thus completes. To move on to the second light amountadjustment, the laser source 62 turns on after the time (T4+T5) (StepS63) and the APC control is started (Step S64) in this embodiment. Atthis stage, the deflection mirror surface 651 has already turned aroundand the scanning light beam (second light beam) is heading for theeffective image region IR.

As in the second embodiment, the scanning light beam (second light beam)moves toward the effective image region IR, and when the scanning lightbeam moves passed the sensor position (the angle of amplitude θs), thesensor 60A outputs the horizontal synchronizing signal Hsync as thesecond detection signal. This results in the “YES” decision at Step S7so that the sequence proceeds to Step S8 and the APC control ends.

After the time T6 since turning on of the laser source 62 (Step S9), thelight source drive signal falls down to the L-level and the laser source62 turns off (time T7; Step S10). The sequence then returns to Step S1and the next latent image forming operation is started based on thedetection signal Hsync. In other words, in synchronization to thedetection signal Hsync, the light source drive signal corresponding tothe image signal is fed to the laser source 62 from the light sourcedriver 1021 and the laser source 62 turns on in accordance with theimage signal (time T8). As a result, a latent image corresponding to theimage signal is formed in the effective image region IR of thephotosensitive member 2.

As described above, in the third embodiment as well, the amount of thelight beam L is thus adjusted while the light beam is successivelyscanning and a latent image is being formed within the effective imageregion IR, and therefore, the latent image is formed stably, which issimilar to the second embodiment. Further, since the third embodimentrequires turning off the laser source 62 while the angle of amplitude θof the deflection mirror surface 651 holds (θs<θ≦θmax), the latent imageis formed even more favorably. In short, at a position outside the firstscanning area SR1 (the angle of amplitude θ:θir<θ<θmax), the lasersource 62 turns on only when needed for detection of the horizontalsynchronizing signal Hsync and adjustment of the amount of light, butthe laser source 62 remains otherwise turned off. This preventsdevelopment of stray light at a position outside the first scanning areaSR1 after detection of the first detection signal Hsync, and effectivelysuppresses formation of a ghost image. It is therefore possible to forma more favorable latent image within the effective image region IR.

Although the APC control (adjustment of the amount of light) is executedover two stages in the third embodiment, either one of the two stagesmay be performed. Alternatively, the APC control may be executed overthree or more stages.

<Others>

The present invention is not limited to the embodiments above, but maybe modified in various manners in addition to the preferred embodimentsabove, to the extent not deviating from the object of the invention. Forinstance, although the sensors 60A and 60B are disposed at the bothedges of the second scanning area SR2 in the first through the thirdembodiments above, the number and the arrangement of the sensors are notlimited to this. As shown in FIG. 12 for instance, one horizontalsynchronization sensor 60C and return mirrors 69 c through 60 e may beused for detection of the scanning light beam.

Further, although the deflection mirror surface 651 which oscillates ismade using a micro machining technique in the embodiments above, themethod of manufacturing the deflection mirror surface is not limited tothis. The present invention is generally applicable to any image formingapparatus in which a deflection mirror surface which oscillates deflectsa light beam and the light beam scans on a latent image carrier.

Although the invention has been described with reference to specificembodiments, this description is not meant to be construed in a limitingsense. Various modifications of the disclosed embodiment, as well asother embodiments of the present invention, will become apparent topersons skilled in the art upon reference to the description of theinvention. It is therefore contemplated that the appended claims willcover any such modifications or embodiments as fall within the truescope of the invention.

1. An image forming apparatus, comprising: a latent image carrier whichhas an effective image region over a predetermined width along a mainscanning direction; a latent image forming section which, using adeflection mirror surface which oscillates, makes a light beam from alight source reciprocally scan a second scanning area which is widerthan a first scanning area which corresponds to the effective imageregion along the main scanning direction, and guides the scanning lightbeam in the first scanning area toward the effective image region,thereby forming a latent image in the effective image region; a detectorwhich is disposed outside the first scanning area but within the secondscanning area, outputs a first detection signal when a first light beammoves past the detector, and outputs a second detection signal when asecond light beam moves past the detector, the first light beam beingthe scanning light beam traveling away from the effective image region,the second light beam being the scanning light beam traveling toward theeffective image region; and a controller which controls a latent imageforming operation based only on the first detection signal which isoutputted from the detector and not on the second detection signal. 2.The image forming apparatus of claim 1, wherein the light beam ismodulated in accordance with an image signal so that a latent imagecorresponding to the image signal is formed in the effective imageregion, and the controller controls a timing to start the modulation ofthe light beam in accordance with the first detection signal.
 3. Theimage forming apparatus of claim 1, wherein the controller executes thelatent image forming operation after confirming oscillations of thedeflection mirror surface based on the first detection signal and thesecond detection signal which is outputted after the first detectionsignal from the detector.
 4. The image forming apparatus of claim 3,wherein the controller stops the latent image forming operation whenoscillations of the deflection mirror surface are not confirmed.
 5. Theimage forming apparatus of claim 3, wherein the controller makes thelight source turn off after the first detection signal is outputted fromthe detector, keeps the light source turned off, and makes the lightsource turn on again so that the second light beam moves past thedetector.
 6. The image forming apparatus of claim 1, wherein the firstscanning area is located approximately at the center of the secondscanning area and the detector is disposed one each at each edge of thesecond scanning area.
 7. The image forming apparatus of claim 1, whereinthe deflection mirror surface resonates.
 8. An image forming method foran image forming apparatus which comprises a latent image carrier whichhas an effective image region over a predetermined width along a mainscanning direction and a latent image forming section which, using adeflection mirror surface which oscillates, makes a light beam from alight source scan a second scanning area which is wider than a firstscanning area which corresponds to the effective image region along themain scanning direction, and guides the scanning light beam in the firstscanning area toward the effective image region, thereby forming alatent image in the effective image region, the method comprising thesteps of: detecting a first light beam which is the scanning light beamtraveling away from the effective image region; inverting the deflectionmirror surface and accordingly making a second light beam scan andtravel toward the effective image region following the first light beam;and controlling the operation of forming a latent image with the secondlight beam, in accordance with the result of detection of the firstlight beam.